Ants and Plants: Symbiotic Living

The first known farmers were apparently…ants. Leafcutter ants have been growing fungus on chopped up leaves for at least 50 million years. It is an amazingly long time.  Yet, when one thinks of the astonishing range of different “breeds” of animals and crops which humankind has created through artificial selection during the 10 millenia or so years since we started farming, the ants seem a bit lackluster.  For all of their workaholic zeal, ants are not as relentless as us in selecting for traits in their crops.

Yet, as we learn more about the ants and their empire, the amazing extent of their symbiosis with the plants they use is beginning to become more apparent to us.   Because of the vastly greater timeline of their endeavors, they have coevolved in astonishing ways. An example of this can be found in the homes of Philidris nagasau, a species of leaf cutterant native to Fiji.  These ants literally grow their homes out of Squamellaria, an epiphytic plant which grows on tropical trees.

The Economist described the mechanism through which the ants grow a home (or, alternately, the way the epiphytic plant obtains an army of insect servants):

P. nagasau worker ants harvest seeds from their epiphytic homes, carry them away, and then insert them into cracks in the bark of suitable trees. That done, they patrol the sites of the plantings to keep away herbivores, and also fertilise the seedlings as they grow by defecating into hollow structures called domatia that develop in the bases of the plants’ stems. As a Squamellaria grows, its domatium swells (see picture) and develops galleries that can accommodate ants—which then move in. This, and the plant’s habit of growing flowers that generate nectar long after they have been pollinated, provide the evolutionary quid pro quo that makes the relationship between insect and epiphyte work.

It is incredible that the ants grow their own houses.  Yet, as one looks more closely at familiar domestic arrangements with this story in mind, they start to seem less familiar.  Is farming really as unique as we make it out to be, or does it resemble mutualistic arrangements found throughout the natural world.

We would never say we co-evolved with goats, cows, and horses: their domestication seems like a one way exchange to us. Yet an outside observer might look at our leather sofas, cheeseburgers, cavalry charges, or angora sweaters and come to a different conclusion.